Limit the number of devices we delete at once (#14649)

synapse/handlers/device.py

@@ -458,10 +458,12 @@ class DeviceHandler(DeviceWorkerHandler):
 
     async def _prune_too_many_devices(self, user_id: str) -> None:
         """Delete any excess old devices this user may have."""
-        device_ids = await self.store.check_too_many_devices_for_user(user_id)
+        device_ids = await self.store.check_too_many_devices_for_user(user_id, 100)
         if not device_ids:
             return
 
+        logger.info("Pruning %d old devices for user %s", len(device_ids), user_id)
+
         # We don't want to block and try and delete tonnes of devices at once,
         # so we cap the number of devices we delete synchronously.
         first_batch, remaining_device_ids = device_ids[:10], device_ids[10:]